Coming out of the University of Louisville, where he played college baseball for the Cardinals (where he earned a degree in sports administration),[1] Rosenberg was drafted by the Philadelphia Phillies in the 13th round of the 2008 draft. He spent the following three seasons in the lower levels of the Phillies' farm system, acting primarily as a closer. Between 2008 and 2010, he recorded 33 saves in 48 games while posting a 12–4 record between three levels despite being briefly sidelined with a latissimus dorsi injury.[2]

He opened the 2011 season with the AA Reading Phillies, where he briefly served as a starting pitcher. That season, he recorded a 4.17 ERA with a 5–7 record in 39 games. After again opening the 2012 season with the Reading Phillies, he was promoted to the Triple-A Lehigh Valley IronPigs.

On June 9, 2012, he was added to the Philadelphia Phillies' 25-man active roster.[3] He made his Major League debut that same day against the Baltimore Orioles.